Hi, first of all i have to see your website, and you want to completely system in the app right? Definitely i cannot develop under $250. A mobile app has lot of works, hope you understand.. I will develop using ionic framework it used to develop hybrid mobile app. We can create iOS and android simultaneously. You are asking for payment integration, login with facebook and gmail. see lot of features you need and another thing you want to integrate with the existing website. Please understand the work and i tell you honestly it will cost around $1200. If you are interested we will work. I will show daily updates, i will send the apk you can install in mobile and check the update. Thank you. Raj